Text Diff Checker

Features

• Word-level or line-level comparison
• Additions and deletions colour-coded inline
• Optional whitespace and case insensitivity
• Similarity percentage and change counts
• Copy a plain-text unified summary

How to use it

1. Paste the original version on the left.
2. Paste the changed version on the right.
3. Choose word or line granularity.
4. Green marks additions, struck-through red marks deletions.

How the comparison works

This uses a longest common subsequence algorithm, the same foundation as diff and Git. It finds the longest sequence of tokens appearing in both texts in the same order, then treats everything else as either an insertion or a deletion. That produces a minimal, readable set of changes rather than simply reporting that everything after the first difference changed.

Word granularity is best for prose, where a single edited word inside a long paragraph should not mark the whole paragraph as changed. Line granularity matches how code review tools work and is better for source files, configuration and any text where line boundaries carry meaning.

The similarity percentage is the proportion of tokens unchanged relative to the longer of the two texts. It is a rough guide rather than a precise measure of semantic similarity, reordering two paragraphs produces a low score even though nothing was truly added or removed. For large inputs the algorithm is capped at 4,000 tokens per side, since LCS cost grows with the product of both lengths.